/*
 * @(#)VariableDefinition.java
 *
 * Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 *   1. Redistribution of source code must retain the above copyright notice,
 *      this list of conditions and the following disclaimer.
 * 
 *   2. Redistribution in binary form must reproduce the above copyright
 *      notice, this list of conditions and the following disclaimer in the
 *      documentation and/or other materials provided with the distribution.
 *
 * Neither the name of Sun Microsystems, Inc. or the names of contributors may
 * be used to endorse or promote products derived from this software without
 * specific prior written permission.
 * 
 * This software is provided "AS IS," without a warranty of any kind. ALL
 * EXPRESS OR IMPLIED CONDITIONS, REPRESENTATIONS AND WARRANTIES, INCLUDING
 * ANY IMPLIED WARRANTY OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE
 * OR NON-INFRINGEMENT, ARE HEREBY EXCLUDED. SUN MICROSYSTEMS, INC. ("SUN")
 * AND ITS LICENSORS SHALL NOT BE LIABLE FOR ANY DAMAGES SUFFERED BY LICENSEE
 * AS A RESULT OF USING, MODIFYING OR DISTRIBUTING THIS SOFTWARE OR ITS
 * DERIVATIVES. IN NO EVENT WILL SUN OR ITS LICENSORS BE LIABLE FOR ANY LOST
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 * OF LIABILITY, ARISING OUT OF THE USE OF OR INABILITY TO USE THIS SOFTWARE,
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 *
 * You acknowledge that this software is not designed or intended for use in
 * the design, construction, operation or maintenance of any nuclear facility.
 */

package org.wso2.balana.cond;

import org.wso2.balana.Indenter;
import org.wso2.balana.ParsingException;
import org.wso2.balana.PolicyMetaData;

import java.io.OutputStream;
import java.io.PrintStream;

import org.w3c.dom.Node;
import org.w3c.dom.NodeList;

/**
 * This class supports the VariableDefinitionType type introuced in XACML 2.0.
 * It allows a Policy to pre-define any number of expression blocks for general
 * use. Note that it's legal (though not usually useful) to define expressions
 * that don't get referenced within the Policy. It is illegal to have more than
 * one definition with the same identifier within a Policy.
 * 
 * @since 2.0
 * @author Seth Proctor
 */
public class VariableDefinition {

	// the identitifer for this definition
	private String variableId;

	// the actual expression defined here
	private Expression expression;

	/**
	 * Creates a new <code>VariableDefinition</code> with the given identifier
	 * and expression.
	 * 
	 * @param variableId
	 *            the identifier for this definition
	 * @param expression
	 *            the expression defined here
	 */
	public VariableDefinition(String variableId, Expression expression) {
		this.variableId = variableId;
		this.expression = expression;
	}

	/**
	 * Returns a new instance of the <code>VariableDefinition</code> class based
	 * on a DOM node. The node must be the root of an XML
	 * VariableDefinitionType.
	 * 
	 * @param root
	 *            the DOM root of a VariableDefinitionType XML type
	 * @param metaData
	 *            the meta-data associated with the containing policy
	 * @param manager
	 *            <code>VariableManager</code> used to connect references to
	 *            this definition
	 * 
	 * @throws ParsingException
	 *             if the VariableDefinitionType is invalid
	 */
	public static VariableDefinition getInstance(Node root,
			PolicyMetaData metaData, VariableManager manager)
			throws ParsingException {
		String variableId = root.getAttributes().getNamedItem("VariableId")
				.getNodeValue();

		// get the first element, which is the expression node
		NodeList nodes = root.getChildNodes();
		Node xprNode = nodes.item(0);
		int i = 1;
		while (xprNode.getNodeType() != Node.ELEMENT_NODE)
			xprNode = nodes.item(i++);

		// use that node to get the expression
		Expression xpr = ExpressionHandler.parseExpression(xprNode, metaData,
				manager);

		return new VariableDefinition(variableId, xpr);
	}

	/**
	 * Returns the identifier for this definition.
	 * 
	 * @return the definition's identifier
	 */
	public String getVariableId() {
		return variableId;
	}

	/**
	 * Returns the expression provided by this definition.
	 * 
	 * @return the definition's expression
	 */
	public Expression getExpression() {
		return expression;
	}

	/**
	 * Encodes this class into its XML representation and writes this encoding
	 * to the given <code>OutputStream</code> with no indentation.
	 * 
	 * @param output
	 *            a stream into which the XML-encoded data is written
	 */
	public void encode(OutputStream output) {
		encode(output, new Indenter(0));
	}

	/**
	 * Encodes this class into its XML representation and writes this encoding
	 * to the given <code>OutputStream</code> with indentation.
	 * 
	 * @param output
	 *            a stream into which the XML-encoded data is written
	 * @param indenter
	 *            an object that creates indentation strings
	 */
	public void encode(OutputStream output, Indenter indenter) {
		PrintStream out = new PrintStream(output);
		String indent = indenter.makeString();

		out.println(indent + "<VariableDefinition VariableId=\"" + variableId
				+ "\">");
		indenter.in();

		expression.encode(output, indenter);

		out.println("</VariableDefinition>");
		indenter.out();
	}

}
